1. Field
One or more aspects of embodiments according to the present invention relate to improving the quality of synthetic aperture radar images and more particularly to methods for generating navigation profiles resulting in improved image quality.
2. Description of Related Art
Ground penetration radar (GPR) typically operates at low frequency because higher frequencies have a significantly diminished ability to penetrate the ground. When operated from a platform, such as an aircraft, capable of carrying only a small antenna, the low frequency, i.e., long wavelength, results in a wide antenna pattern.
The use of synthetic aperture radar (SAR) makes it possible to generate radar images with high spatial resolution using a small antenna on a moving platform. SAR signal processing techniques accomplish this by combining the signals received by the moving antenna at various points along its path in such a way as to simulate the operation of a larger antenna, having dimensions comparable to those of the path of the small antenna.
To construct sharp SAR images it is necessary to have more accurate information about the path of the antenna than may be available, for example, from a path estimator based on a global positioning system receiver and on an inertial navigation system (a GPS/INS system). Prior art systems may generate improved images using an autofocus algorithm after first dividing the image into sub-images, or image blocks, and then finding values of the second order range corrections for which the focus is best. These systems may, if large image blocks are used, suffer from discontinuities at the boundaries between image blocks. If small image blocks are used, then some may contain low quality targets and the results of the autofocus algorithm may be poor.
Therefore, there is a need for a new solution to refocus SAR images.